1. Field of the Invention
This invention concerns a control circuit for an AC plasma display panel.
Such plasma display panels are familiar in the prior art, for example in French patent application No. 78 04893, publication No. 2 417 848, filed on behalf of THOMSON-CSF, and in the article published in Revue Technique Thomson-CSF, June 1978, vol. 10, No. 2, pp. 249-275.
These panels comprise a large number of cells, arranged in matrix formation. Each cell is formed by the gas space at the intersection of two electrodes belonging to two orthogonal electrode networks, and receives control signals consisting of the difference in voltages reaching the two electrodes between which it is located.
Control signals comprise setting signals, to light the cells, erasure signals, to extinguish them, and maintenance signals, to keep the cells in their initial state, on or off.
2. Description of the Prior Art
In the prior art there are control circuits for AC plasma display panels, to issue panel control signals. The article already referred to mentions plasma display panel control circuits comprising a multiplexing network, which helps reduce the number of amplifiers needed to establish selective signals, i.e. setting and erasure cells.
This multiplexing network can be obtained by providing each electrode with two diodes and a resistor.
However, control circuits involving a multiplexing network have the following drawbacks:
since they contain a large number of amplifiers or transistors, resistors and condensors, they are bulky, and energy-consuming; PA0 it is difficult to control several electrodes simultaneously. PA0 a logic circuit receiving instructions in low-voltage logic, defining the signal to be implemented, its duration, and the panel electrodes to be addressed; PA0 a low-voltage/high-voltage interface circuit, controlled by the logic circuit, which receives DC voltages of 0 and 100 volts, and which comprises means of supplying each display panel electrode with two different voltages, 0 and 100 volts, depending on the instruction delivered to the logic circuit. PA0 compactness; PA0 ease of addressing: the user issues instructions in low-voltage logic, and applies a DC voltage of 100 volts to the integrated circuits, instead of having to cope with high-voltage crenellations; PA0 possibility of simultaneously addressing as many electrodes as required. PA0 the technology used for integrated circuits on the market at present restricts the amplitude of output signals to 100 volts, whereas maintenance signals are crenellated voltages which normally range from -100 to +100 volts; this means that power supplies to integrated circuits connected to one of the electrode networks have to be made to "float" on crenellations with an amplitude of 100 volts; PA0 control signals delivered by these circuits are voltage crenellations, so that it is no longer possible to obtain erasure and setting signals comprising a voltage gradient, as shown in FIGS. 3a and 4 of the patent application already referred to, whereas it is very useful to be able to use such erasure and setting signals, since this permits erasure and setting without the need to make delicate adjustments because of scattering of cell characteristics; PA0 finally, the output resistance R.sub.on of the output amplifiers of these integrated circuits is much higher (approximately 100 times greater) than for discrete amplifiers, causing a sharp reduction in the luminance of plasma display: for large panels it may even cause a loss of recorded data. PA0 compactness; PA0 ease of addressing in low-voltage logic, and simultaneously addressing of several electrodes. PA0 energy consumption for this circuit is less than for a control circuit using only integrated circuits, because only non-integrated amplifiers are in action when maintenance signals are being issued; PA0 the invention uses integrated circuits with an output signals amplitude of 200 volts, so that it is no longer necessary to make power supplies "float", as has to be done with integrated circuits on the market, which have an output signal amplitude of not more than 100 volts; PA0 the circuit can issue erasure and setting signals containing a voltage slope; PA0 there is no loss of luminance or data in plasma display panels using the control circuit proposed in this invention, even though the output resistance of amplifiers in the integrated circuits used is high: only non-integrated amplifiers are used to issue maintenance signals; such amplifiers are usually constructed using bipolar technology and have a low output resistance R.sub.on ; on each alternation of the maintenance signal, a discharge current passes through each lit cell, reversing the memory voltage of the cell; the circuit used to issue maintenance signals must be capable of delivering or accepting this discharge current, which is a few tens of microamps per lit cell, during 0.1 to 0.2 .mu.s, without the maintenance signal being deformed; consequently, the circuit to issue maintenance signals must have a low output resistance, and this applies to this new control circuit: when setting or erasure signals are being issued there is no or almost no discharge current, so that such signals can easily be issued by integrated circuits with high output resistance.
An article published by TEXAS INSTRUMENTS in November 1980, Bulletin SCA-204, entitled "A. C. Plasma Display", describes integrated circuits involving "BIDFET" technology, used to control AC plasma display panels.
These integrated circuits comprise a single housing, which contains:
The advantages of these integrated circuits, compared with circuits composed of discrete components, are as follows:
However, these integrated circuits involve the following disadvantages: